Anti-side-tone substation circuit



l Jari. 27. 1925.

F. W. MCKOWN ANTI SIDE TONE sUBsTATIoN CIRCUIT Filed July 17. 191e.

y Magi Patented Jan. 27, 1925s UNITED STATES FREDERICK w. NexowN, or New Yoan, N.

COMPANY, INCORPORATED, or New Yoan,

Y., essisNoR To wRs'rnR-N ELECTRIC N. Y., a. ConroRArIoN or NEW YORK.

ANTIQSIDEeTONF. SUBSTTION CIRCUIT.

Application filed July 17, 1919. Serial BT05311543.

To all whom if; may concern.'

Be it known that l, FREDERICK W. MC- KowN, `a citizen otthe United States, residing at New York, in the county ot `New York, State of New York, have invented certain new and useful lmproven'ients in Anti-Side-Tone Substation Circuits, of which thetollowing is a Vfull, clear, concise, and exact description.

This invention relates to anti-side-tone telephone substation circuits.

An object of 'the invention is to provide a telephone-substation which will be anti-sidetone without the' employment ot a trans former yand which will .permit the energization of the transmit-ter by current from a common battery.

`For thispurpose a two-windingreceiver is employed land the transmitter, line wires and in the preferred `form an auxiliary impedance vare so connected to these windings that, on transmitting, the alternating current is divided between the two windings in such a way -that the ampere turns in the windings are substantially equal and opposite so that the current produces substantially fno -eiiect on the receiver diaphragm. On receiving, `currents from the line may pass through the windings in such a man- `ner that their effects on the Vreceiver will be ata maximum. Preferably the relations are such that on receiving substantially no current flows in the auxiliary impedance nor in the winding associated therewith.

A further object `ot the invention isfto design a circuit of the above type which will "be specially adapted for use in a hand set substation. Under some conditions it may be desirable to -locate inthe ringer box the condenser or `condensers necessary for controlling the tlow of direct current and for balancing the capacity of the line. In the 'form of the invention rwhich it is preferred to use/where possible a single condenser in `the ringer` box serves thethree fold function of preventing direct current from being shunted around the transmitter, providing a path for ringing currents and balancing thecapacity of the line.

These and other objects of the invention will be more ltully understood from the following detailed description and claims taken in connection with the accompanying drawings 1n which Fig. 1 is a diagrammatic representation of one form of my invention;

Fig. 2 is a modiiication in which a `single condenser takes the place oi' the two condensers shown in Fig. 1;

Fig. 3 is a modification in which two condensers are placed in the ringer box;

Fig. 4 is acircuit diagram illustrating the :tlow of currents in transmitting;

Fig. 5 is a similar view illustrating the ow ot currents in receiving;

Fig. 6 is a circuit diagram showing` the invention applied to a bi-polar receiver; and

Fig. 7 is a schematic showing ot the circuit employed in Fig. 2.

Referring to the drawings by reference numerals, the hand set 10 comprises the transmitter 11 and the receiver 12. On the receiver core 13 are two windings 14 and 15, their adjacent ends being connected by conductor 16 to the transmitter 11. rFhe winding 1,4 may be partially or wholly formed of resistance wire for a purpose which will be explained later on.

The leads 17 and 18 from windings 14 and 15 'are connected to the apparatus in the ringer box 19 by the cord conductors 20 and 21 respectively, conductor 2O being connected directly to line wire 22. Conductor 21 is adapted to be connected to the other line wire 23 when the hand set is removed 'from the hook 24.

The transmitter 11 is connected by lead 25 to lead 17 at Q6, and it will be seen that Vthe transmitter is energized by direct current from the central battery indicated at 27. A condenser 28 is provided to prevent the fiow of direct current in the branch of the circuit including winding' 14 and also to balance the capacity of the line as will be later explained. The ringer 29 and conlenser 30 are bridged directly across the The operation of the circuit of Fig. 1 will be more easily understood from the simplified diagrams of Fig. 4 and Fig. 5. The impedance ot the line as seen troml the substation generally consists of a resistance component and a small capacity component. The resistance 31 is designed to balance the resistance of the line and the condenser 28 to balance the capacity of the line. Fig. 4 shows the direction of current flow on transmitting. The current divides between windings 14 and 15. The ratio ot these windings to each other and the relation of the impedance of the auxiliary resistance and condenser 28 to the impedance of the line are so designed that the ampere turns in the two windings are equal, thus producing substantially no eiect on the receiver diaphragm. For the purpose of saving space the auxiliary resistance 31 is preferably incorporated in the winding 14, as above stated. K y

The current flow on receiving, as shown in Fig. 5, is through the transmitter 11 and winding 15, substantially no current 'flow-- ingV through' auxiliary resistance 31 and winding 14.- on account ot the voltage iuduced in winding 1lV by the current in winding 15. Considerable variation from this condition, however, can' be had without greatly interfering' with the eiiiciency oi the set. Reference is made to U. S. Patent to George A. Campbell, 1,254,472, January 22, 1918, for a discussionV of the general principles involvediin designing substation Vcircuits employing an auxiliary resistance which conjugate to the impedance of the line.. As pointed out in this patent the impedance of the transmitter should besuch with respect to the impedance of the line and the other elements of the substation circuit, that the transmitter in operating, works into an impedance approximately equal to its own impedance.

In case it is not feasible to place the condenser 28 in the hand set, the arrangements shown in Fig. 2 or Fig. 8 may be employed. In Fig. 2 the single concenser 28 is so positioned that it is in series with the ringer when the hook 24. is down, and also in a series circuit with winding 14 when the hook is up. In this arrangement terminal 26 corresponds to terminal 26 in Fig. 1, conductor 25 being extended to the ringer box and an additional switch 32 being provided to break the circuit through the transmitter when the substation is idle. This arrangement is shown schematically in VIhe arrangement of Fig. 3 is like that of Fig. 1 except that the condenser Q8 is placed in the ringer box and the conductor 25 is extended from the transmitter to the rmger box.

The operation of the circuits of Figs. `2 and 3 is substantially identical with that of Fig. 1. 'Y K Y y In Fig. 6 the Vinvention is shown applied to a substation having a Yreceiver with a bipolar magnet 23. Since in this form thereI is negligible mutual impedance between the receiver windings, the balancing resistance 31 may behomitted and absence of sidetone may be secured by properly proportioning the number of turns in each winding.

While the circuits disclosed herein are adapted for use in any telephone substation wherein the transn'iitter is energized by current from a. central station, they are particularly well adapted for use in substations employing handsets, in which there is inherently a greater tendency to singing be cause of the mechanical connection between the receiver and the transmitter.

lVhat is claimed is:

1. In combination with a common battery telephone line, a side tone reduction substation circuit comprising two branches, a telcphone transmitter in a conductor common to said branches and adapted to be energized by direct current from the common battery, a telephone receiver having a magnetic core, a. plurality of differentially wound windings on said core each of said branches having directly included therein one of said windings, one of said branches beingadapted -to be connected to the line, and the other of said branches formingV a closed loop, the individual portion of said other branch having sufticient impedance to balance the line included in said first branch, said transmitter having such an impedance with respect to the line and the other elements of the suhstation circuit, that the transmitter when operated works into an impedance of the order of the impedance of the transmitter.

2. In combination with a. common battery telephone line, an anti-side-tone substation circuit comprising two branches, a telephone transmitter in a conductor common to said branches and adapted to be energized by direct current from the common battery, a telephone receiver having a magnetic core, a plurality of differentially wound windings on Vsaid core. each of said branches having directly included therein one of said windings, one of said branches being adapted to be connected to the line, and the other of said branches forming a closed loop, the individual portion of said otherbranch having sufficient resistance to balance the resistance of the line. and suliicicnt capacity to balance the vcapacity of the line, the elements of said Ycircuit having such impedance, and being so arranged that currents from the transmitter do not appreciably actuate the receiver, and currents received from the line do not appreciably fiow through the individual rtion of said other branch, said transmitter having such an impedance with respect to the line and the other elements of the substation circuit. that the transmitter when operated works into an impedance of the order of the impedance of the transmitter.

3. An anti-side-tone substation circuit comprising two branches, a receiver having a plurality of differentially wound windings, one of said windings being included in each of said branches, one of said branches being adapted to be connected to a line, and the other of said branches forming a closed ioop, said closed loop comprising a series condenser, and a ringer' adapted to be connected across said line, said condenser being so loca-ted as to prevent the How of direct current through said ringer.

4. An anti-side-tone substation circuit comprising two branches, a receiver having a plurality of dii'erentiaily Wound Windings, one of said windings being included in each of said branches, one of said branches being adapted to be connected to a line, the other of said branches forming a close-d loop, said closed ioop comprising a series condenser, a ringer adapted to be connected across said iine, said condenser being so located as to prevent the How of direct current through said ringer, and a transmitter in a conductor common to said branches and adapted to be energized by direct current` from said line.

5. In combination with a telephone line, a substation set comprising a transmitter and receiver, switching means for connecting to or disconnecting from the line said transmitter and said receive-r, a shunt path around said transmitter when the transmitter is connected. to the line, a ringer, a condenser in series with said ringer and the line, and contacts and connections operated when said transmitter and said receiver are connected to the line for connecting said condenser in said shunt path for preventing direct current from being shunted around said transmitter.

6. A telephone circuit having two branches one of said branches comprising a line and the other of said branches comprising a resistance designed to balance the resistance of Said line and a condenser designed to balance thel capacity of said line, a receiver Winding in each of said branches, and means for producing a flow of direct current in said rst circuit branch.

In Witness whereof, I hereunto subscribe my name this 14th day of July, A. D. 1919.

FREDERICK W. MOKOWN. 

